Turbine draft tube



Sept. 1, 1936. 1 COGPER 2,052,555

TURBINE DRAFT TUBE Filed March 5, 1955 j 3 Sheets-Sheet l lNVE-NTOR HOWARD L. COOPER ATTORNEY Sept. 1,1936. COOPER 2,052,555

" TURBINE DRAFT TUBE v Filed March 5, 1955 s Sheets-Sheet 2 FIG.2

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I'NVENTOR HOWARD L. COOPER ATTORNEY Sept. 1, 1936. H. COOPER N 0 L. COOPER HOWARD RNEY I:

val/( ATTO Patented Sept. 1, 1936 iUNlEi) STATES PATENT OFFIQE 4 Claims.

(Granted under the act of March 3, 1883, as amended April 30, 1928; 370 0. G. 757) This invention described herein may be manufactured and used by or for the Government for governmental purposes, without the payment to me of any royalty thereon.

This invention relates in general to the art of regaining some of the residual velocity head in the water, lost upon leaving the hydraulic turbine in a form of increased efficiency of the hydraulic turbine. It is a well recognized fact that on account of the function which is fulfilled by the draft tube, it is properly regarded as an integral part of the turbine. Therefore, considering the turbine and draft tube as a unit, it may be seen that the less. the kinetic energy lost through the tube, the higher the efficiency of the wheel.

The total power available is that due to the total head from head water level to tail water level. The power of the turbine is less than this by an amount equal to that lost in the intake, penstock, draft tube, mechanical friction and hydraulic loss. Anything which reduces the loss outside the turbine adds just that much more to the power which, the water can give up within the turbine.

Further, the total energy remaining in the water at the'runner end of the draft tube depends not only upon the elevation of this point above or below the tail water level but also upon the velocity head of the water at that section minus the friction and hydraulic losses to be lost within the draft tube, including the residual velocity head at its'discharge. The less these losses, the higher the available energy at the runner, the better will be its performance.

Among the causes contributing to low efliciencies of the usual elbow or horizontal types of draft tube are the following:

Failure to divide water evenly in horizontal discharge channels.

Water leaving turbine runner with an induced whirl which continues to the end of the draft tube, causing air pockets, surging and uneven velocities.

The primary object of my invention is to transfer the flow in the draft tube from a turbulent, whirling flow to a smooth, straight flow nearly parallel to the draft tube walls.

A further object of my invention is to accomplish this change in flow within the shortest distance possible.

A still further object is to regulate the flow in my draft tube so that resistance to flow is a minimum with the results of a more efficient turbine operation.

Another object is to produce a draft tube of such form that its length may be materially reduced without affecting its efficiency.

I attain these objects by shaping the draft tube Walls as illustrated in the accompanying drawings in which:

Fig. 1 is a vertical cross-section through the draft tube and i Fig. 2 shows a section taken through the draft tube on the line 2-2 of Fig. 1 with turbine blades omitted: 10

Fig. 3 shows a section taken through the draft tube on the line 33 of Fig. 1, where tube is beginning to assume a bulbous contour;

' Fig. 4 shows a section taken through the draft tube on line l-4 of Fig. 1, in which view an elonl5 gation of the bulbous portion is shown;

Fig. 5 shows a section taken through the draft tube on the line 5-5, here the bulbous sections have been elongated still further and a sectionof a centrally located pier which divides the draft tube into two conduits, is shown; I

Fig. 6 shows a section taken through the draft tube on the line 66. In this locality the separated conduits are assuming a rectangular shape of greater cross-sectional area than those shown in Fig. 5;

Fig. 7 shows a section taken through the draft tube on the line 'l-1. In this view the separate conduits have been increased in area and are square in shape; V

Fig. 8 is a section taken on the line 88 and shows the inner edge of the centrally located pier which divides the outlet portion of the tube into two conduits.

Similar numerals refer to similar parts throughout the several views.

Any turbine runner, running in counter-clockwise direction gives to the fluid a counter-clockwise whirling component as it discharges from the runner into section 2-2. 40

The bulbous portions of the turbine draft tube from section 22 to 3-3 serve as collecting channels, in which much of the whirling or retating motion is dissipated and the flow partially straightened.

From section 3-3 to 4-4 the change from a rotating motion to a straight line flow has nearly been completed.

Any turbine runner, running in a clockwise direction with a clockwise whirling component, will have similar but opposite-hand collecting channels.

The drawings are shown for counter-clockwise operation of the runner.

The draft tube as shown in the illustration said tube with a plane passed through the central axis normal to said first mentioned vertical plane, 2

would outline lateral boundaries of theiinternal surface of said tube which gradually diverge from the inlet to the outlet opening, as indicatedby the sectional views illustrated in Figs. 2 to 7 inclusive. From about the center of the elbow a vertically disposed central pier (l0) divides the tube in two separate conduits. entire length of the tube from the inlet opening to the outlet opening the cross-sectional contour of the interior surface is as follows: In the inlet portion of the tube which extends from the sections 2'2=i.shown in Fig. 2 tothe section 44 shown in'Fig. 4 the tube gradually changes its contour from a circular form in the vicinity of the turbine blades to an elongated form with a restricted center and bulbous extremities, forming collecting channels [2 and I 2' on either side of the restricted central portion. The bulbous contour, indicated throughout the various views by the numerals II and II, is more'pronounced in the direction of the flow, which is indicated by the arrows. This contour continues throughout the 'elbow' wherein the central pier (l0) (Fig. 8) is formed, said pier continuing as a partition Wall throughout the'outlet portion of the draft tube and dividing the collecting channels l2 and I2 intotwo-separate conduits. Within the separate conduits the bulbous contour becomes less and less pronounced as the interior of the conduits assume a rectangular shape, as shown in the sectional'view in-Figures 5 to 7 inclusive.

Throughout the-entire length of the draft tube the direction of the particles or molecules of the fluid stream is gradually changed from a circular whirling motion at the inlet opening to a longitudinal movement at the outlet.

Having described myinvention what I claim as new and wish to secure by Letters Patent is:-

1. A turbine draft tube adapted for the receptionof fiuid in a whirling stream, and means interior said tube comprising diametrically opposite collecting channels of bulbous cross-sectional Throughout the portion, adapted to progressively change rotary motion of a fluid passing therethrough into a straight line flow.

3: A turbine draft tube, comprising an inlet portion, an outlet portion and an intermediate elbow, means in connection with the inner surface of the bore of said tube adapted to convert the rotary movement of the fluid passing through the tube into a direct line flow, theconversion being eifectedwithin a limited area between the inlet and outlet openings of the tube, said means comprising laterally disposed collecting channelsof bulbous contour located on either side of a restricted central portion, extending wi thin the inlet portion, the elbow and the outlet portions of said tube. v r V 4. A turbine draft tube composed of aninlet portion, an outlet portion, and an intermediate elbow, the contour of the intersection of said tube with a vertical plane passed throughits central axis outlining boundaries of the interior surface of said tube which gradually'converge from the inlet opening to the elbow, and gradually diverge from theelbow to the outlet opening, and the contour of the intersection of said tube witha plane passed through the central axis normal to said first mentioned plane, outlining boundaries of the internal surface of said tube which gradu ally diverge from the inlet to the outlet opening; a central vertically disposed pier extending from. the elbow to the outlet opening, 'dividing' the outlet portion of the tube intoseparate'conduits, the interior contour of the tube from the. inlet opening to the pier being formed with gradually enlargingbulbous channelson each side of a con-,

stricted central portion, and from the beginning of the pier'to the outlet opening; separate cone duits in which the channels of bulbous contour are continued, their, contour becoming less pronounced as the conduits approach. their outlets. s

HOWARD L. COOPER. 

